Method and apparatus for guiding a moving tape

ABSTRACT

Method and apparatus for guiding a moving tape having a tape edge parallel to a direction of motion of the tape wherein the tape is received tangentially on a curved surface having an edge. Force applied to the tape is increased as the tape drifts farther away from a nominal position so as to move the tape away from the edge of the surface. Lateral motion of the tape is dampened by breaking up an air-cushion between the tape and the curved surface.

BACKGROUND

Information is recorded on and read from a moving magnetic tape with amagnetic read/write head positioned next to the tape. The magnetic“head” may be a single head or, as is common, a series of read/writehead elements stacked individually and/or in pairs within the head unit.Data is recorded in tracks on the tape by moving the tape lengthwisepast the head. The head elements are selectively activated by electriccurrents representing the information to be recorded on the tape. Theinformation is read from the tape by moving the tape longitudinally pastthe head elements. Magnetic flux patterns on the tape create electricsignals in the head elements as the tape moves along. These signalsrepresent the information stored on the tape.

Data is recorded on or read from each of the parallel tracks on the tapeby positioning the head elements at different locations across the tape.Head elements are moved from track to track, as necessary, either torecord or to read the desired information. A head position actuatoroperatively coupled to servo control circuitry controls movement of thehead according to servo information recorded on the tape. A tape driveusually includes head positioning actuators. A head positioning actuatoroften includes a lead screw driven by a stepper motor, a voice coilmotor, or a combination of both. The head is supported by a carriagethat is driven by the actuator along a path perpendicular to thedirection of tape travel. The head elements are positioned as close tothe center of a track as possible based upon the servo information.

Servo circuitry is better able to position a head properly with respectto a tape if the lateral position of the tape is suitably restricted.Tape guides with flanges often are used to restrict the position of thetape. Flanges, however, can cause excessive wear on the edge of thetape. Conversely, the sharp edges of the tape can, over time, causeexcessive wear on the flange, itself. The tape sometimes curls at theedges when it touches the flange. This curling further destabilizes thelateral position of the tape.

As the speed of tape drives continues to increase, another factor hasbeen noted that contributes to lateral tape motion. This factor is a“ground-effect” that results from a film of air that can form betweenthe tape and the guide. This film of air acts to decrease the frictionbetween the tape and the guide. The tape then tends to float and towobble laterally. In some cases, the reduction in friction even causesthe tape to ripple across the lateral dimension of the tape.

SUMMARY

Method and apparatus for guiding a moving tape having a tape edgeparallel to a direction of motion of the tape wherein the tape isreceived tangentially on a curved surface having an edge. Force appliedto the tape is increased as the tape drifts farther away from a nominalposition so as to move the tape away from the edge of the surface.Lateral motion of the tape is dampened by breaking up an air-cushionbetween the tape and the curved surface.

BRIEF DESCRIPTION OF THE DRAWINGS

Several alternative embodiments will hereinafter be described inconjunction with the appended drawings and figures, wherein likenumerals denote like elements, and in which:

FIG. 1 is a flow diagram that summarizes a representative embodiment ofa method for guiding a moving tape;

FIG. 1A is a diagram of a mathematical model of one representativeembodiment of a corner of a tape guide;

FIG. 1B is a diagram of a mathematical model of an alternativeembodiment of a corner of a tape guide;

FIG. 2 is a pictorial diagram of an exemplary embodiment of a tapeguide;

FIG. 2A is a diagram showing detail of an exemplary embodiment of adampening apparatus; and

FIG. 3 is an edge view of a representative embodiment of tape rollerguide.

DETAILED DESCRIPTION

FIG. 1 is a flow diagram that summarizes a representative embodiment ofa method for guiding a moving tape. The tape in this embodiment has anedge parallel to the direction of motion of the tape. According to thepresent method, the tape is received tangentially on a curved surface(step 5). A force is applied to the tape edge to counter drift as thetape drifts from a nominal position (step 10). The applied forceincreases as the tape drifts farther away from its nominal position. Thepresent method still further comprises dampening the lateral motion ofthe tape by breaking up an air-cushion that can form between the tapeand the curved surface (step 15). Lateral motion of the tape is motionof the tape in a direction perpendicular to the direction of motion ofthe tape as the tape moves over the curved surface.

FIG. 1A is a diagram of a mathematical model of one representativeembodiment of a corner of a tape guide. According to one alternativevariation of the present method, a force is applied to the tape edgethat increases approximately linearly with the distance of the tape fromits nominal position. According to another alternative embodiment, asurface 25 of a tape guide is represented by an x-axis 27. A flange 30disposed at the edge of the surface 25 of the tape guide is representedby a y-axis 32. A linear transition 35 joins the surface 25 of the tapeguide to the flange 30. According to another alternative embodiment, alinear transition 35 results when the corner between the flange 30 andthe surface 25 of the tape guide comprises a chamfer. Mathematicalequation 37y=d−x   (37)represents the straight line corresponding to the linear transition 35.When a magnetic tape moves to a position 40 where the edge of the tapehas left the surface 25 of the tape guide and has begun to ride up onthe linear transition 35, mathematical equation 37 indicates to whatlevel of elevation the edge of the tape will rise above the surface 25of the tape guide. If the edge of the tape is more than a distance d 60from the edge of the flange 30, then the tape does not rise up at all.For distances less than d 60 from the edge of the flange, thenmathematical equation 37 applies.

According to one embodiment, a flange is disposed on the edge of thecurved surface. The position of the flange is a convenient referencepoint for defining the location of the edge of the tape. For example,with the tape in position 40, the edge is a distance x1 46 from theflange. Mathematical equation 37 states that the edge of the tape risesto an elevationy 1=d−x 1(y1 has reference designator 48 in FIG. 1A) above the surface 25 of thetape guide. The tape in a tape drive normally is kept under tension, sowhen the tape edge rides up on a transition like the linear transition35 in this example, the tape stretches slightly. This stretch causes aslight increase in the tension of the tape that produces a reactionforce f_(R) 41 that acts downward toward the surface 25. As the edge ofthe tape rides upward along the linear transition 35, the edgeexperiences two force components (42, 44) that are applied at rightangles to each other at the edge of the tape. The lengths of the arrowsrepresenting forces (42, 44) in FIG. 1A are not intended to beproportional to the force represented. The horizontal component 44 ofthe force at the edge of the tape tends to direct the tape back into itsproper position as the reaction force f_(R) 41 acts to drive the tapeback against the surface 25. In the case of the horizontal forcecomponent 44, the tape has not moved very far from its proper position,so only a small force is applied to the edge of the tape.

When the tape moves to a position 50 farther from its nominal positionthan position 40, then the same considerations apply. The edge of thetape in this example is a distance x2 56 from the flange 30 where x2 isless than x1. Mathematical equation 37 states that the edge of the tapenow rises to an elevationy 2=d−x 2(y2 has reference designator 58 in FIG. 1A) above the surface 25 of thetape guide. Elevation y2 58 is greater than y1 48, so the tape undergoesa stretch greater than the stretch corresponding to y1 48. Accordingly,the increase in the tension in the tape is greater, and the forces (52,54) applied to the edge of the tape are greater than the forces (42, 44)corresponding to y1. The horizontal component 54 of the force applied tothe edge of the tape tends to direct the tape more forcefully toward itsproper position than was the case corresponding to y1 48.

FIG. 1B is a diagram of a mathematical model of an alternativeembodiment of a corner of a tape guide. According to this alternativeembodiment, a curved transition 65 joins the surface 25 of the tapeguide to the flange 30. One example embodiment of a curved transitioncomprises a circular arc 65 defined by the mathematical equation 67y=d−{square root}{square root over (d ² −(x−d) ² )}.   (67)Mathematical equation 67 indicates to what level of elevation the edgeof the tape will rise above the surface 25 of the tape guide accordingto this example embodiment. As was true for the linear transition, ifthe edge of the tape is more than a distance d 60 from the edge of theflange 30, then the tape does not rise up at all. For distances lessthan d 60 from the edge of the flange, then mathematical equation 67applies.

The circular arc 65 tends to provide more gentle treatment for an out ofposition tape than does the linear transition 35 shown dotted in FIG. 1Bfor convenience. For example, with the tape in position 70, the edge isa distance x1 76 from the flange. Mathematical equation 67 states thatthe edge of the tape rises to an elevationy 1=d−{square root}{square root over (d ² −(x1−d) ² )}(y1 has reference designator 78 in FIG. 1B) above the surface 25 of thetape guide, less than the rise in elevation corresponding to lineartransition 35. Consequently, the increase in tension of the tape is lessthan the increase obtained with the linear transition 35. This resultsin less reaction force f_(R) 41 acting downward toward the surface 25.The resulting forces (72, 74) applied to the edge of the tape with thecurved transition are correspondingly less than the forces (42, 44)applied with the linear transition 35.

When the tape moves to a position 80 farther from its nominal positionthan position 70, then the same considerations apply. The edge of thetape in this example is a distance x2 86 from the flange 30 where x2 86is less than x1 76. Mathematical equation 67 states that the edge of thetape now rises to an elevationy 2=d−d ²−{square root}{square root over ((x 2−d)²)}  (67)(y2 has reference designator 88 in FIG. 1B) above the surface 25 of thetape guide. Elevation y2 88 is greater than y1 78. Therefore, the tapeundergoes a stretch greater than the stretch corresponding to y1 78.Accordingly, increase in the tension in the tape is greater, and theforces (82, 84) applied to the edge of the tape are greater than theforces (72, 74) corresponding to y1 78. The horizontal component 74 ofthe force applied to the edge of the tape tends to direct the tape moreforcefully toward its proper position than was the case corresponding toy1 78. The force 74 corresponding to the circular arc 65 is less thanthe force 44 corresponding to the linear transition 35, againdemonstrating the more gentle treatment of the tape with the circulararc 65.

Other types of transitions besides the linear transition 35 and thecircular arc 65 are possible. The examples presented here are only forillustration and should not be interpreted as an intention to limit thescope of the appended claims. For example, transitions combining bothstraight and curved portions are contemplated. Further, the transitioncould comprise multiple straight sections or curvatures with increasingor decreasing degrees of slope or curvature, respectively.

As already described, a film of air (i.e. air-cushion) can form betweenthe tape and the curved surface in some embodiments of high-speed tapedrives. Consequently, the tape may have a tendency to “float” above thecurved surface. This floating effect reduces the friction between thecurved surface and the tape thereby allowing lateral motion of the tape.The present method dampens lateral motion of the tape by breaking upair-cushion between the tape and the curved surface. According to oneexample embodiment, this breaking up of the air-cushion is accomplishedby directing or channeling air away from the surface of the tape guideat a plurality of locations. According to one alternative embodiment,the number of locations is two. According to another alternativeembodiment, the number of locations is three. According to yet anotheralternative embodiment, the number of locations is four. According tostill one more alternative embodiment, the number of locations is five.These locations and corresponding structure are discussed in more detailwith reference to FIGS. 2 and 3.

FIG. 2 is a pictorial sectional diagram of an exemplary embodiment of atape guide. This embodiment of a tape guide is capable of guiding amoving tape. This embodiment comprises a curved surface 125 that iscapable of tangentially receiving a moving tape. The embodiment furthercomprises restrictors capable of restricting the position of the tape onthe curved surface. One example of restrictors comprises a first flange131 and a second flange 132 disposed on opposite ends of the curvedsurface. The flanges (131, 132) form nominal right angles with thecurved surface 125. The flanges (131, 132) operate to impede the lateralmotion of a tape moving in a direction 135 parallel to the flanges (131,132).

FIG. 2A is a diagram showing detail of an exemplary embodiment of adampening apparatus. This detail is a close-up view of the corner thatdefines the intersection between the curved surface 125 and the firstflange 131 described in the discussion of FIG. 2. The corner is notsquare, but, rather, has the shape of a curved transition 150 capable ofapplying a force to an edge 155 of a tape 160 as the tape moves awayfrom its nominal position and approaches first flange 131. As the tapemoves farther away from its nominal position and farther up thetransition 150, the force applied to the tape increases. It should beunderstood that a substantially similar corner defines the intersectionbetween the curved surface and second flange 132.

As described in the discussion of FIG. 1A and FIG. 1B, other types ofcurved transitions 150 are available. One embodiment of the tape guidecomprises a linear transition or “chamfer.” The linear transitionoperates as described in the discussion of FIG. 1A. Another embodimentof the tape guide comprises a circular arc. The circular arc operates asdescribed in the discussion of FIG. 1B. Other types of curvedtransitions are possible as discussed above in connection with FIGS. 1,1A and 1B. The linear and circular examples presented herein should notbe interpreted as a limitation on the appended claims.

FIG. 2 further illustrates that one alternative embodiment furthercomprises friction enhancers between the tape and the curved surface.Friction enhancers operate in one embodiment by partitioning anair-cushion layer that can form between the tape and the curved surface.According to one alternative embodiment, friction enhancers comprisegrooves 140 disposed in the curved surface 125 in a direction 135nominally parallel to the direction of motion of the tape. According toone particular alternative embodiment, the grooves 140 are V-shaped andact to channel air away from the curved surface at three locations.According to another alternative embodiment, two grooves are provided.According to yet another alternative embodiment, four grooves areprovided. Still one more alternative embodiment of the tape guidecomprises five grooves disposed in the curved surface 125.

FIG. 3 is an edge view of a representative embodiment of tape rollerguide. This representative embodiment is capable of guiding a movingtape. The present embodiment of the tape roller guide 200 comprises ahub 205. The hub 205 has a cylindrical curved surface 210. Thecylindrical curved surface 210 is capable of tangentially receiving atape. The embodiment further comprises first and second flanges (230,232). Flanges (230, 232) function as range restrictors capable ofrestricting the position of the tape edge on the cylindrical curvedsurface 210 of the hub 205.

The present embodiment further comprises dampeners 250 (depicted inFIGS. 1A, 1B and 2A), said dampeners 250 comprising corners that definethe intersection of the cylindrical curved surface 210 and the flanges(230, 232). The corners are configured to apply progressively more forceto an edge of the tape as the edge of the tape moves through a cornertoward a flange. One example embodiment of the dampeners 250 issubstantially identical to the transition 150 described in thediscussion of FIGS. 1B and 2A. In another alternative embodiment of thedampeners, the transition 150 comprises a circular or rounded cornerformed with a radius substantially in the range of 0.03 mm to 0.5 mm.This exemplary range is provided to illustrate, but not limit the scopeof the appended claims. In yet another alternative embodiment of thedampeners, each transition 250 comprises a chamfer disposedsubstantially as described in the discussion of FIG. 1A. As alreadydescribed, other curved transitions 250 are possible, and the examplespresented herein are not intended to limit the scope of the appendedclaims.

The first flange 230 extends out from a first end 207 of the hub.Likewise, the second flange 232 extends out from a second end 208 of thehub opposite the first end 207. Together, first and second flanges (230,232) act to restrict the position of the tape edge on the cylindricalcurved surface of the hub.

According to one embodiment, the tape guide roller 200 further comprisesa plurality of grooves 240 disposed in the curved surface 210 of the hub205. The grooves 240 act as friction enhancers. The grooves 240 act toenhance friction between the tape and the curved surface 210. Accordingto one alternative embodiment, grooves 240 are V-shaped having a widthsubstantially in the range of 0.2 mm to 0.6 m and a depth substantiallyin the range of 0.1 mm to 0.3 mm. One alternative embodiment of the tapeguide roller comprises two grooves. Another alternative embodimentcomprises three grooves. Yet another alternative embodiment comprisesfour grooves. Still one more embodiment of the tape guide rollercomprises five grooves. Again, any ranges stated herein are for thepurposes of illustration and are not intended to limit the scope of theappended claims.

While the present method, tape guide, and tape guide roller have beendescribed in terms of several alternative methods and exemplaryembodiments, it is contemplated that alternatives, modifications,permutations, and equivalents thereof will become apparent to thoseskilled in the art upon a reading of the specification and study of thedrawings. It is therefore intended that the true spirit and scope of theappended claims include all such alternatives, modifications,permutations, and equivalents. One such variation would include theintroduction of spiral grooves or other geometrically shaped grooves.Such grooves are intended to be included in the scope of the appendedclaims.

1. A method of guiding a moving tape having a tape edge parallel to adirection of motion of the tape, said method comprising: receiving thetape tangentially on a curved surface having an edge; applying a forceto the tape to move the tape edge away from the edge and towards anominal position, wherein the force applied increases as the tape driftsfarther away from the nominal position; and dampening lateral motion ofthe tape by breaking up an air-cushion between the tape and the curvedsurface.
 2. The method of claim 1 wherein applying a force to the tapecomprises: applying a force that increases approximately linearly with adistance of the tape from the nominal position.
 3. The method of claim 1wherein applying a force to the tape comprises: applying a force thatincreases approximately as a square root of a difference between asquare of the nominal distance of the tape edge from the edge of thecurved surface and a square of a distance of the tape edge from the edgeof the curved surface.
 4. The method of claim 1 wherein breaking up anair-cushion comprises: directing air away from the curved surface at aplurality of locations.
 5. The method of claim 4 wherein the pluralityof locations is selected from the group consisting of two, three, four,and five.
 6. A tape guide capable of guiding a moving tape having a tapeedge parallel to a direction of motion of the tape, said tape guidecomprising: means for receiving the tape on a surface having an edge;and means for applying a force to the tape edge to counter drift as thetape drifts from a nominal position, wherein the force applied increasesas the tape drifts farther away from its nominal position.
 7. The tapeguide of claim 6 wherein the force applying means comprises: a curvedtransition between the edge and the surface.
 8. The tape guide of claim6 wherein the force applying means comprises: a curved surface with auniform radius of curvature.
 9. A tape guide roller comprising: hubhaving a curved surface; range restrictors capable of restricting aposition of a tape edge on the curved surface of the hub; dampenerscapable of dampening lateral motion of the tape on the curved surface ofthe hub; and friction enhancers capable of enhancing friction betweenthe tape and the curved surface of the hub.
 10. The tape guide roller ofclaim 9 wherein the range restrictors comprise: first flange extendingout from a first end of the hub; and second flange extending out from asecond end of the hub.
 11. The tape guide roller of claim 10 wherein thedampeners comprise: corners defining an intersection of the curvedsurface of the hub and the first flange, and an intersection of thecurved surface of the hub and the second flange, each corner configuredto apply progressively more force to an edge of the tape as the edge ofthe tape moves through the corner toward a flange.
 12. The tape guideroller of claim 11 wherein each corner comprises a curve.
 13. The tapeguide roller of claim 12 wherein the curve is circular.
 14. The tapeguide roller of claim 13 wherein the circular curve has a radiussubstantially in a range of 0.03 mm to 0.5 mm.
 15. The tape guide rollerof claim 11 wherein each corner comprises a chamfer.
 16. The tape guideroller of claim 9 wherein the friction enhancers comprise a plurality ofgrooves disposed in the curved surface of the hub.
 17. The tape guideroller of claim 16 wherein the grooves are V-shaped having a widthsubstantially in the range of 0.2 mm to 0.6 mm and a depth substantiallyin the range of 0.1 mm to 0.3 mm.
 18. The tape guide roller of claim 16wherein the number of grooves is selected from the group consisting oftwo, three, four, and five.